Process and apparatus for making metal powder



` Aug. 19,'1941. E. J. HALL 2,252,714

PROCESS AND APP'AATUS FOR MAKING METAL POWDER Filed June 29, 1957Sheets-Sheet l Ham/fr L. HALLbr/a/x BY Aug. 19, 1941. E, J, HALLV2,252,714 Y PRocEss AND APPARATUS FoR MAKING METAL POWDER Filed June29, A937 2 sheets-sheetg 2 al 'ATTORNEY5 Patented ^Aug. 19, 1941 UNITEDSTAT Es PATENT o FFICE raooass AND APPARATUS Foa MAKIN METAL POWDEREverett J. H all, deceased, late of Elizabeth, N. J., by Harriet L.Hall, executrix, Elizabeth, N. J., assigner to Metals DisintegratingCompany, Inc., Union Township, Union County, N. J., a corporation of NewJersey Application June 29, 1937, Serial No. 150,934 l (Cl. l-'12) `1eclaims.

This invention relates to the production of copper powder by reducingoxides of copper and then breaking up the resultant friable mass ofmetallic copper. While not restricted thereto, the invention isparticularly adapted to the production of copper powder for bronzebearings and other molded objects.

- In manufacturing bearings from copper powder, other materials (e. g.tin and/or graphite)` cooling of the batch furnace necessaryto reducethe temperature of the newly formed copper powder below the oxidationpoint. Furthermore, the batch procedure is limited as to the control ofthe reduction obtainable to produce y powder to meet differentspecifications, and to are often mixed with the copper. Large pro-'ducers of bearings use automatic pressing ma-- chinery equipped withautomatic filling devices. To insure uniform bearings and continuousperformance of the pressing machinery, the bearing material must haverequisite iiowability.

underthe molding pressure must be uniform. After the bearing has beenmolded, it is sintered or heat treated; and the` size of the bearing isAd.-v `ditionally, the compressibility of the material changed by thismanufacturing step. If the'20 `heat treated bearing is too short it mustbe l scrapped; if it is too long, it must be ground down,as the bearingmaterial does not machine satisfactorily. Thus, the bearing materialmust produce a powder which uniformly meets a given specification. Amongthe general objects of the present invention are to provide a moreeilicient and economical process for reducing copper oxides to formcopper powder, to provide a process which can be adequately varied toproduce powder to meet different specifications, to provide a proc- Yess which can be adequately controlled to produce A,copper powder havinguniform predetermined` characteristics, and to provide apparatussuitable for such improved processes.

Various specific and detailed objects of the iiivention will be apparentto those skilled inthe k art from the disclosure herein of the preferredbe Vsuch that a uniform and predetermined change of size will take placewhen the bearing is sintered. Furthermorep the finished bearing l musthave sufficient strength; and the bearing material must be such4 as willgive the strength.

From the foregoing it will be seen that the bearing Imanufacturerrequires a copper powder. which is exceedingly uniform as to the variousphysical characteristics that affect the manufacture of the bearing. Andthese physical characteristics must be correlated with the pressing.35

fdies, iilling machinery, other ingredients added by the bearingmanufacturer, size and type of bearing to `be made, etc. T he result isthat the manufacturer of the copper powder is `called upon to meet awide range of powder specicafw tionssubmitted by bearing manufacturers;and, as` to each specification a uniform powder must be supplied.

VHeretofore copper powder has been made in batches. Trays containingthin layers of oxides of copper were placed in a chamber or furnacewhich was then closed and reducing gas passed therethrough. After thereduction had been effected the resultant copper` powder (and the batchchamber) had to be cooled sufficiently to 50 prevent the powder frombeing oxidized by contact of the air. l

This prior art batch procedure is inefficient and wasteful because (a)to get the desired dethe reducing gasmust be discharged before itsreducingv constituents are substantially oxidized, (b)` the batchreducing furnace cannot be recharged immediately, but must be iirstcooled,-

and (c) there is a large net heat loss due-to the` .gree of completenessof reduction of thel oxidesf form of the invention.

In its preferred form the invention comprises i a process ofcontinuously reducing oxides in a muil-le furnace, but the improvementis not merely that vordinarily obtained by changing from batch procedureto continuous procedure. In various other manufacturing lines batchprocesses have been quickly replaced by continuous processes, but thathas not been the case with the manufacture' of copper powder by thereduction of copper oxides. oxide requires treatment of a powder with agas;

and this does not readily lend itself to a continuous process, owing tothe fact that a powder cannot be introduced or withdrawn through agastight trap, as can be done with a liquid. On the other hand, it hasbeen found, in accordance with the present invention, that there arechemical factors which can be so utilized in an appropriate continuousprocess as to overbalance the disadvantages inherent` in continuoustreatment of a powder with a gas. These chemical factorsl will now bepointed out.

The rate of reduction of cupric and cuprous Y out at this time thatcontinuous operation en-n ables the temperature to be controlled incread The reduction of copper 0f course, a hard cake is unde Furthermore,too high lreduction tem- Vapor in the gas.

f vantageously, as wellas permitting the material treated to be raisedmorequickly to proper reducing temperature, and subsequently -cooledmorerapidly and Veconomically below the atmospheric oxidation point. i

,When a reducing 'gasfis used which contains both carbon monoxide andhydrogen, a number of reactions occur:

Thereductionof the oxides of copper is added, catalytically, by thepresence of freecopper and is retarded, catalytically, by the presenceof water At temperatures around 200 C., theinhibiting action of Watervapor is very pronounced. While such 'action decreases as thetemperature rises, it is a factor to be reckoned =with at1400 C., andeven at 450 to 550 C.

Accordingly, reactions 1) and (3) catalyze themselves,lwhile reactions(2) and (4) inhibit themselves. Reaction (5) takes place readily at450.,to 550 C., particularly in the presence of a readily oxidized thanCO and Hz, so that, if the reducing gas used has any considerablehydrocarbon content, a part of the gas may to advantage be recirculatedtoy give the residual hydrol to condense the water vapor formed and thenrecirculate. f

As in' the case of the batch process, it is ordinarily advisable to usea mixture of cuprous copper Ywill'ordinarily be present with the oxidescatalyst so that while CO is present in the gas in any considerableyconcentration, the `water vformed is largely eliminated. i

'I'hese facts, coupled withthe mass action laws, Amake it especiallydesirable to carry out the reduction countercurrent. The .fresh reducinggas with maximum content of C and Hz and a minimum content of H2Ostrikes the nearly re duced oxide when the tendency for the reversiblereactions:

toproceed to the right is a maximum according to the mass action law inview of the fact that, at such time the ratios Cu': CuO and Cu CuzO arevery high. The presence ofthe reduced copperalso aids in overcoming thenormal tendency of the mass action law to retard further reduction.

Due to reaction mentioned above, the water vapor does not reachseriously high con' centrations until afterA the gas and powder havemoved countercurrent a considerable distance and the ratio of Cu CuO orCu CuzO has dropped to the point at which mass action law ceases to bean important factor, so far as the solid components ofthe reactions areconcerned.

The heats of reaction are. such that when a reducing gas containing bothCO and I -h are brought into contact with copperoxides at 450 to ,550C., there is a strong tendency for the CO t\obe converted into CO2before `appreciable amounts of-water vapor are formed. The heats ofoxidation of copper, carbon monoxide and hydrogen are as follows:

Calories Cu+O 34,900 2 Cu+o 39,900 CO-|O v 67,960V 2 H--O 57,826

Consequently, if a gaslcontaining both carbon i monoxide and hydrogen isbrought into counter,- current contact with copper oxides, the latterwill pass iirst through a zone in which the hydrogen is the chiefreducing agent and then through a,

and cupric oxides, the proportions usually ranging from 60 to 90% CuzO,with a complementary amount of lCuO, allowance being made for the freecopper present withlthe oxides. Some free matically, by way of example,inthe accompany- I ing drawings, in which:

Fig. 1 is a longitudinal vertical section through the muiile furnace inwhich the reduction takes place; f

Fig. 2 is a Iside elevation of the cooling section of theapparatus;

Fig. 3 is a section on the line 3-3 of Fig. 1; Fig. 4 is -a detail viewof the feed end of the muiile' furnace 'with water extracting apparatusconnected thereto; y

Fig. 5 isa detail section on the line 5--5 of Fig. 2:

Fig. 6 is a'detail section Fig.' 2; and

Fig. 7 is a detail section on the line 'I-I of Fig. 6.

'I'he apparatus vcomprises two main parts, a

on the lines-6.61

4heating and reducing section (shown in Fig.'1) l and a cooling section(shown in Fig. 2).' Inthe ilrst section the mixed oxides are heated toaround 450' to 550 C. in a reducing atmosphere to convert the oxidesinto metallic copper, and in is a fiat steel belt I0 passing overpulleys Il, II,

one of which is driven by any suitable means not shown. Preferably, thebearings of one pulley s' are movable and are biased to tension thebelt.

The upper half of the belt "is wholly enclosed in a iiattened steelcasing designated as a whole by I2, open at both ends and composed of alplurality of sections which are bolted and welded together.

The tube I2 may be considered as having `four operating zones orsections I2a, I2b, I2c, and

I2d. The feed end I2a of this casing is provided with a hopper I3 formixed oxides. vA vertically adjustable gate I4 regulates the thicknessof the layer of oxides carried forward by the belt and also serves tosome extent as a closure to prevent ,escape of reducing gas or entry ofatmospheric air, according to the manner in which the ap ratus isoperated. Some gas can and will pass in or out through the intersticesof the powder on the belt, according to the relative pressure in andoutside the casing.

After leaving the hopper the belt passes under a series of pivotallysupported weighted bars I (see also Fig. 3 which serve to form furrowsin the oxide layer for the dual purpose, first of aiding the reduction,and second of rendering thev friable mass of reduced copper more easilybroken and pulverized.

Attached to the casing section I2a above-the bars l5 is a fiue IB forthe discharge of spent reducing gases. The adjoining portion |2b of thecasing forms the inner chamber of a muilie furnace. Surrounding `thissection of the casing is at around 425 to 450 C., 450 t 500 C., 475 to550 C., and 400 to 425 C., respectively. These ytemperatures are givenmore as a general guide for average operation and not 4as fixed rangesnever to be departed from. Thus, where slow reduction is desired, thetemperatures may be reduced, and vice versa.

Beyond the furnace section is the gas-introducing and gas-preheat'ingsection |2c, to which is connected a pipe 24 for supplying thereto cityor other suitable reducing gas. In addition to the pipe 24, other pipes,as 25 and 2G, may be used to supply further amounts of reducing gasdirect to the furnace section 12b.

. Ordinary coal gas contains preponderating proportions of hydrogen andmethane and only a small amount of carbon monoxide. Such gas is not assuitableas city gas composed inpart of water gas and hence having a highproportion of carbon monoxide. A gas of this type which has been foundto give good results has the following approximate composition:

The gas-introducing section I2c is connected `to the cooling section |2dby a gate valve 29 comprising a vertically slidable gate (Fig. 6) whichmay be raised and lowered by turning the Vhand- `wheel 3| at the upperend of a threaded rod 32.

'I'he gate is set so Athat it just clears the layer of `reduced copperon the belt i0 and thereby acts been deoxidized by kburning oil in it orby passing it over red hot coke or the like. Such gas is often referredto as DX" gas. It may be slightly reducing, which is preferred for thepresent purpose. Alternatively, an actively reducing gas may be used,such as ordinary city gas. Also, a part or all of the spent reducing laspassing up the ue I6 may'be supplied to the pipe 34, but it is rstpreferably cooled below '70 C.

'I'he non-oxidizing gas ilows along the cooling section in the samedirection as the belt moves therethrough and is drawn on through a flueadjacent the discharge end of the casing.

As the belt I0 passes over the pulley Il it contacts with one edge of ahopper 36 and the repassing it through a condenser to eliminate the.

greater part of the water vaportherein. An attachment for recirculatinga part of the reducing gases after condensing out the majority of thewater is shown in Fig. 4. A centrifugal blower 40 draws gas from thecasing section I2a through pipe 4i and discharges it through condenser42 and pipe 43 back to the gas inlet pipe 24. A valve-controlled by-pass44 enables the amount of gas re-circulated to be regulated.'

Good results have been obtained with a muiile furnace section 35 feetlong, a cooling section of i8 feet, and a belt speed of 5 to 20 feet perhour, depending on the rate of ow of the reducing gases, depth of oxidelayer on the belt, temperature in the reducing zone, and other factors.An

as a constriction in the casing to prevent flow of v gas therealong atthat point.

33,50 that by the time the reduced copper on the The cooling sec- `tion`is provided with one or more water jackets A't the e'nd of the coolingsection I2d adjacent the gate valve is an inlet pipe 34 for somesuitablenon-oxidizing gas, such as` air which has average speed underpresent commercial practice is 8 feet, per hour. Changing the rate ofreduction has a marked influence on the properties of the finishedproduct. Slow reduction gives lower density, liner particle size andlower ilow than rapid reduction.

In operating the apparatus reducing gas is introduced through the pipe24, flows countercurrent to the direction of movement of the belt I0through casing sections |2c and i2b and is discharged up the flue I6. Asthe spent gas Ainevitably contains small amounts of carbon monoxide, itis desirable to apply sumcient `suction to the tube IS/so that thegaseous pressure at .the bottom of the flue is slightly belowatmospheric and sdrne air is drawn in under the gate I4. For the samereason, it is desirable to put slight suction on the flue 35 to preventany non-oxidizing gas passing out into the room where the apparatus islocated. To this end fiues I6 and 35.

may be connected to a chimney which is heated to produce a draft. Inaddition, or in the alternative, suction may be'produced by eductor jetsISa and 35a. Butterfly valves `Ilib and 35D provide furtherv control.

'I'he mixed oxides passing through the casing sections |2b and I2c arefirst heated to the temperature of reduction, then pass through a zonein which hydrogen isthe chief reducing agent, next through a zone inwhich carbon monoxide is the chief reducing agent and nally through azone in-which the hot reduced copper preheats the reducing gases.

In compliance with the patent statutes, the best known forms of theinvention have been disclosed, but it will be understood that thedisclosure is illustrative and not limiting.

what reiaim is:

phere in the second section `of the casingpand 1. An apparatus forproducing a friable mass of copper, comprising an endless moving belt, atubular casingsurrounding the upper section of the belt, means fordepositing a layerof copper oxides on the belt at the feed end of thecasing, gas discharge fiues adjacent each end of the casing, aconstriction near the -middle,

of the casingfor preventing the ow of gas along the casing at thatpoint, means for introducing reducing Agas on the feed side of suchconstriction for countercurrent flow with respect, to the movement ofoxides by the belt, means for introducing non-oxidizing gas on thedischarge side of such restriction for flow in the same direction as themovement ofthe belt, and means for cooling the reduced copper onthe-belt between such constriction and the discharge endofthe casing.

2. In the art of reducing copper oxides by causing a continuousribbon-like stream of the comminuted oxides to travel horizontally anduninterruptedly through a furnace and thence, without change of form ordirection, through ,a cooling chamber that is in communication with thefurnace, the improvement which consists in supplying reducing gas to thefurnace and causing it to make contact with the oxides` in` the furnaceand to move horizontally counter-current to the direction of travel ofthe oxide stream; in applying to the furnace, at selected intermediatepoints along itsv length,`means for establishing within the furnace inconnection with the reaction, heat inside the` furnace, differentselected temperatures at such selected intermediate points, andcontrolling the temperature-` establishing means by means responsive `to`fluctuations in the temperatures, to compensate for such fluctuations,whereby those 'tempera-` tures are substantially maintained despitevariations in reaction heat; in supplying non-oxidizing gas to thecooling chamber and causing it to travel in the same direction as theoxide stream;

- and in` substantially preventing thev movement of gas from the furnaceinto the cooling chamvber and from the cooling chamber into the furnace.i

3. The method of producing a-friable mass of metallic copper, comprisingpassing a continuous `horizontally moving stream of reducing gas over acontinuous. longitudinally scored ribbon-like stream of heated copperoxides moving horizontally in the oppositeI direction, and thereaftercausing the stream of copper to travel rwithin a stream of coolnon-oxidizing gas moving in the direction oftravelof the copper stream,while -preserving the crossesectional dimensions: of the streamthroughoutj its travels. i

4. An apparatus for producing a friable mass of copper, comprising anendless moving belt whose upper course is disposed and travelshori--zontally, a tubular casing surrounding the upper course of the belt,means for supplying to the upper course of the belt, before it yentersthe casing, a layer of copper oxides; a gas outlet V iiue at said end ofthe casing, means located be-` tween the iluefand the oxide supplyingmeans Vfor regulating the thickness of the layer so deposited on thebelt, means forautomatically maintaining different selected temperaturesin different portions of the length of the casing ady jacent its feedend,` means for' cooling a section of the casing adjacent its dischargeend, meansV for maintaining-a reducing atmosphere in` the first namedsection. of the casing, means for maintaining a. coolingand-non-oxidizing atmos` means to prevent mingling of the twoatmospheres.

5. An apparatus for producing a friable massy of copper, comprising anendless movingr belt whose upper course is disposed andtravels'horizontally, a tubularcasing surrounding the upper course ofthe belt and comprising a furnace section into which the upper course ofthebelt first enters, and a communicating cooling section into which thebelt Upasses as it leaves said furnace section, means for depositing alayer of copper oxides on the belt at the outer end of the furnacesection, means for removing reduced copper from the belt at the outerend of the cooling section, a gas discharge ue at the outer end of thefurnace section, a gate located between said iiueand thelayer-depositing means, movable towards and from the belt to regulatethe depth of the layer entering the furnace section, a` second gatelocated, at the junction between the furnace and cooling sections andadjustably fixed to `permit clearance of the oxide stream while offeringan impediment to the movement of gas between the furnace and coolingsections, and means for introducing reducing gas into the inner end ofthe Vfurnace section and on the furnace side of said second named gate.Y i l,

6.An apparatus for producing a friabl'e mass of copper, comprising 'an`endless moving belt whose upper course is disposed and travelshorizontally, a tubular casing surrounding the upper courseof the beltand comprising a furnace section into which the upper course of the beltfirst enters, and a communicating cooling section in 'to which the beltpasses as it leaves said furnace' section, means for depositing a layerof copper oxides on the belt at the outerend of the furnace section,means for removing reduced copper from the belt at the outer end of thecooling section, a gas dischargeflue` at the outer end of the furnacelsection, a gate located between said ue and the layer-depositing means,movable towards and from the belt to regulate the depth of the layerentering the furnace section, a second gate located at the junctionbetween the furnace and cooling sections and adjustably xedto permitclearance of the oxide stream While offering an impediment to themovement of gas between the f furnace and cooling sections, means forintroducing reducing gas into the inner end of the furnace section andon the furnace side of said second named gate, means forintroducingcooling gas into the inner end of` the cooling section and on thecooling section side of said second named gate, and a gas discharge flueat the outer end of the cooling section.

from the belt at the outer end of the cooling sec- A tion, a gasdischarge flue at the outer end of the furnacesection, `a gate locatedbetween said ue and the layer-depositing means, movable towards and fromthe belt to regulate the depth of the layer entering the furnacesection, a second gate located at the junction between the furnace andcooling sections and adjustably fixed to permit clearance of the oxidestream while offering an impediment to the movement of gas between the-furnace and cooling sections, and means for inaasam. l

, reaction heat, and thereafter causing the stream troducing reducinggas into the inner end of the i furnace section and on the furnace sideof said second named gate. .x

8.,A reducing furnaceof the kind described,

comprising a horizontally disposed tubular casing section with anendless belt having its upper course moving horizontally through thecasing section, means for depositing a layer of copper oxides on theupper course of the belt before it enters the casing section, a gate atthe feed end of the'casing section permitting the layer so deposited topass it, but obstructing the movement of gas outwardly from the casingsection, means for introducing reducing gas at the other end of thecasing section, a flue at the said feed end'of the casing section forcausing movement of the gas counter-current to the travel of the belt,means for. heating ythe casing section located `at differentintermediate points along its length, and' vmeans for cooling the casingsection located at A different intermediate` points along its length,said heating and cooling means being thermostatically `controlledsubstantially as and for the purposes set forth.

9.` The method which comprises passing a continuous ribbon-like streamof comminuted copper oxides horizontally and slowly through ahorizontally disposed furnace in an atmosphere of reducing gas, applyingto the furnace at selected intermediate points along the length of thefury nace, means for establishing within thefurnace in connection withthe reaction heat inside the furnace, dierent selected temperatures atsuch selected intermediate points, and controlling thetemperature-establishing means by means responsive to fluctuations inthe temperatures, to

compensate for suchuctuations, whereby those temperatures aresubstantially maintained despite variations in reaction heat.

10. The method which comprises passing a continuous ribbon-like streamofcomminuted copperoxides horizontally and slowly through a horizontallydisposed furnace in an atmosphere of reducing gas movingcountercurrently to the oxide stream, applying to the furnace at.selected intermediate points along the length .of the furof copper totravel, without change of form or direction, within a stream of coolnon-oxidizing gas moving in the direction of travel of the copperstream. g i' 12. Apparatus of the kind described comprising, a tubularhorizontally disposed casing with an endless belt having its uppercourse moving horizontally in the casing, means for continuouslysupplying copper oxides to said belt the casing being divided intoaiurnace section and a cooling section in communication with each other,the

nace, means for establishing within the furnace p intermediate pointsalong the length of the furnace, means for establishing within thefurnace in connection with the reaction heat inside the furnace.4different selected temperatures4 `at such selected intermediate points,controlling the temperature-establishing means by means responsive tofluctuations inthe temperatures', to compensate fory such fluctuations,whereby those temperatures are substantially maintaineddespitevariations in upper course of the belt entering the furnace section andemerging from the cooling section, means for introducing reducing gas atthe junction of the two sections and positively causing it to movetowards and discharge from the outer end of the furnace section, meansfor establishing `within the furnace section, at selected `intermediatepoints` along its length, different selected temperatures at suchselected intermediate points,

means responsive to fluctuations in the temperatures to compensate'forsuch fluctuations and maintain the temperatures substantially constant,and means for introducing non-oxidizing gas at the Junction of thetworsections and positively causing it to move towards and dischargefrom the outer end of the cooling section.

13. The method which comprises passing a continuous ribbon-like stream lof comminuted `copper oxides horizontally .and slowly through ahorizontally disposed furnace in an atmosphere or reducing gas movingcountercurrently to the oxide stream, applying to the furnace, atselected intermediateI points along the length of the furnace, means forestablishing withinthe furnace in connection with the reaction heatinside` the furnace, different selected temperatures within a range ofabout 425 C.-550 C. at' such selected intermediate points, andcontrolling the temperature-establishing. means by means, responsive tofluctuations in the temperatures, to compensate for such fluctuations,whereby those temperatures'are substantially maintained despite`variations in reaction heat; the depth of the copper stream, the speedof its travel, and the rateof flow of the gas being chosen each in viewof the others, whereby eiective reduction of a maximum amount ofmaterial may be accomplished in a given time.

14. The method which comprises passing a continuous ribbon-like streamof comminuted copper oxides horizontally and slowly through a"horizontally disposed furnace in an atmosphere of reducing gas movingcountercurrently to the oxide stream, applying to the furnace, atselected intermediate points'along the length of the lfurnace, means forestablishing within the furnace in connection with the reaction heatinside` the furnace, different selected temperatures within a range ofabout 425 C.550 C. at such selectedintermediate points, controlling thetemperatureestablishing means ,by means responsive to fluctuations inthe temperatures, to compensate for such fluctuations, whereby thosetemperatures are substantially maintained despite variations in reactionheat; the depth of the copper stream, the

speed of its travel, and the rate of ow of -the gas being chosen each inview'of the others, whereby effective reduction of a Imaximum amount ofmaterial may be accomplishedy in a given time; and thereafter continuingto move the metal stream and subjecting it to the action of a stream ofnon-oxidizinggas moving in the direction of, travel of themetal stream.

15. A reducing furnace ofthe kind described comprising a horizontallydisposed tubular casing with an endless belt having its upper coursemoving `horizontally through the casing, means for depositing a layer ofcopper oxides on the upper course of the belt before it entersthecasing,

means for introducing reducing gas at the other end of the casing anddischarging such gas at the feed end of the casing, means forestablishing temperature conditions inside the `furnace, and 10 meansresponsive to temperature fluctuations inside the furnace, controllingsaid temperature- 'establishing means to compensate for such flucltuation's, whereby temperature conditions established inside theYfurnace may be substantially 15- maintained despite variations inreaction heat. v

16. Ihe method which comprises passing a 'continuous ribbon-like streamof comminuted "6 i ci i 2,252,714

copper oxides khorizontally and slowly through a horizontally disposedfurnace in an atmosphere of reducing gas, applying to the furnace atselected intermediate points along the length of. the furnace, heatingand cooling means for establishing Within the furnace in connection with

